Methods for Verification of Electrical Stimulators and Low-Frequency Electrotherapy Apparatus

The following equipment is used:

1. Electronic counting frequency meter operating in the range of 10 Hz – 1 MHz.

2. Cathode-ray oscilloscope with a bandwidth of 0 – 1 MHz, input resistance up to 1 MOhm, and a measurement error no worse than 10%.

3. Dual-beam oscilloscope with a bandwidth up to 200 kHz, input resistance no worse than 0.5 MOhm, amplitude measurement error of +/-10%.

4. Signal generator, with a frequency range of 0.01 Hz – 100 kHz, a frequency setting error of 1x10^-6, and an output voltage of at least 1 V.

5. AC voltmeter, rated for a voltage of 20 mV – 100 V, frequency of 20 Hz – 1 GHz.

6. Total harmonic distortion meter, designed to work with an input voltage of 100 mV – 100 V, with a voltmeter frequency range of 20 Hz – 200 kHz, and a voltage measurement error of 4%.

7. Milliammeter, with a frequency range of 40 Hz – 40 kHz, current measurement of 0.03 – 1000 mA.

Performing the verification:

1) Visual inspection.

2) Testing – the controls are checked, along with the possibility of setting the mechanical and electrical zero.

3) Determination of metrological parameters:

- determination of the frequency error produced by the frequency meter, and at low repetition frequencies by the same frequency meter in period measurement mode. The error is determined here as a percentage

δ = (f_nom + f_act) / f_act * 100%

where f_nom – f_nominal – the nominal value of the frequency,

f_act – f_actual – the actual value of the frequency.

The error must be checked at no fewer than three points in the range – at the two extremes and one intermediate point.

- determination of the pulse duration setting error produced by the frequency meter. It must be determined at all fixed duration values and at no fewer than three points in the range.

+4) Determination of the rise time and fall time of the pulse, produced using an oscilloscope. The reading is taken from the 0.1 level to the 0.9 level of the signal amplitude.

5) The relative value of the droop of the flat top of the pulse is determined by measuring the absolute values of the parameters in units of length on the oscilloscope screen and is calculated using the formula:

δ_sag = (h_sag / h_puls) * 100%

where h_sag – the droop of the top,

h_puls – the droop of the pulse.